1. Field of the Invention
This present invention relates to a method for manufacturing a semiconductor device in which a semiconductor element formed on an insulating surface is peeled.
2. Description of the Related Art
A flexible substrate such as a plastic substrate is superior to a glass substrate in terms of mechanical strength against vibration and impact, and the thickness is easily reduced. In addition, the shape of the flexible substrate has higher possibility compared with a glass substrate. Therefore, various applications of a semiconductor device using the flexible substrate are expected. However, a flexible substrate such as a plastic substrate may often not have such a high heat resistance that it can withstand heat treatment during a step of manufacturing a semiconductor element. Accordingly, a manufacturing method in which a semiconductor element formed over a heat-resistant substrate is peeled and attached to a flexible substrate separately provided has been conventionally employed.
Reference 1 (Japanese Patent Laid-Open No. 8-262475) discloses a technique to form a peeling layer using silicon over a substrate, form an integrated circuit using a thin film transistor over the peeling layer, remove the peeling layer by etching to peel the substrate from the integrated circuit, and then, attach the integrated circuit to another substrate.
However, in the step of manufacturing a semiconductor element, there is a problem that the peeling layer tends to be peeled from the substrate when heat treatment of the peeling layer is performed in the process of manufacturing the semiconductor element. After completing the semiconductor element, the peeling layer is peeled from the substrate in the end; however, it is difficult to continue manufacturing the semiconductor element when the peeling layer is peeled from the substrate before the semiconductor element is completed. Therefore, it is necessary to keep the peeling layer from being peeled from the substrate at least in the phase before the completion of the semiconductor element.
In addition, in manufacturing the semiconductor device which is formed by peeling the semiconductor element, the time spent on the peeling step depends on the speed of etching a peeling layer (etching rate). Thus, the higher the etching rate is, the more rapidly the semiconductor element can be peeled. Accordingly, TAT (Turn Around Time) can be preferably shortened.